Go back to med school.
Echo can show an impaired contractility or reduced ejection fraction.
MRI is MUCH more sensitive to inflammation.
Why not let the cardiologists sort this out.
From Up To Date:
(All contributors for the below are cardiologists)
Cardiac imaging:
•An echocardiogram is performed in all patients with suspected myocarditis to evaluate regional and global ventricular function, valvular function, and other potential causes of cardiac dysfunction.
_____
Maybe you need to read up a bit.